1. Field of the Invention
This invention relates to a maximum frequency detector for limiting the frequency of a digital pulse stream to a certain predetermined maximum frequency, and, more particularly, this invention relates to a maximum frequency detector for limiting the frequency of a digital pulse stream to a certain predetermined maximum frequency by utilization of a counter for preventing the frequency of the digital pulse stream from exceeding the certain predetermined maximum frequency.
2. Description of the Prior Art
Reference is made to U.S. Pat. No. 4,045,887 issued to Nowell on Sept. 6, 1977, and entitled "Switching Regulator Control Circuit". In the Nowell patent, it is desired to control the maximum frequency of a digital pulse stream which is in turn utilized to control the firing rate of a plurality of silicon controlled rectifiers (hereinafter referred to as SCR). The switching regulator, which includes the SCRs, is utilized to convert an unregulated DC voltage to a regulated DC output. It is desirable that, in order not to cause failure of the SCRs, each SCR be allowed to fully recover after firing (i.e., actuation). Therefore, the maximum frequency at which pulses are applied to the firing circuits connected to each SCR must not exceed a certain predetermined maximum frequency. This maximum frequency is approximately equal to the recovery time of the SCR divided by the number of SCRs within the switching regulator circuit. The SCRs are fired in a certain predetermined sequence. The control of the maximum frequency as shown in the Nowell patent is accomplished by allowing the clock generator 100 (FIG. 3) to vary only within a certain limited range in response to the output voltage of the switching regulator circuit.
It has been found in certain applications that a wide range of frequencies is highly desirable. It is also desirable to fire the SCR immediately after recovery when the switching regulator circuit is at 100 percent of the rated load. Therefore, it is desired that very accurate control over the maximum frequency of the digital pulse stream be maintained.
None of the prior constructions of maximum frequency detectors for limiting the maximum frequency of the digital pulse stream produced as known in the art utilizes a counter which prevents the digital pulse stream from exceeding the predetermined maximum frequency.